Answer to Question #6689 in Physical Chemistry for darren

2012-02-21T08:48:35-0500

Question #6689

The mineral hydromagnesite is a hydrated carbonate of magnesium, with the formula Mgx(CO3)y(OH)z.nH2O and a molar mass of 466.0 g/mol. When 1.000g of a pure hydromagnesite is heated to constant mass, solid MgO was obtained. Steam was given off, together with 0.378 g of carbon dioxide. The MgO obtained was then completely dissolved in 50 cm3 of 1.0 mol/dm3 HCl. The resultant solution was transferred into a volumetric flask and diluted to 250 cm3 with deionized water. A 25.0 cm3 aliquot of this solution required 19.00 cm3 of 0.15 mol/dm3 solution of NaOH for complete neutralization.

Calculate the values of x and y. Hence, or otherwise, deduce the values of z and n. Write a balanced equation, including state symbols the thermal decomposition of a pure sample of hydromagnesite.